Photoresist has been applied to silicon wafers in the process of the manufacture of integrated circuit chips, in a number of different ways, and various types of apparatus have been used. In general, photoresist has been applied to such wafers in four different methods. It has been common to lay a wafer on a stationary or revolving surface so as to expose the top of the wafer, and in instances where the wafer is held stationary, the photoresist is applied to the top surface of the wafer by spraying or by applying with a roller. In other instances where the wafer is revolving with the support for it, a few drops or a small stream of photoresist is applied to the center of the revolving wafer, adjacent the rotation axis, and the photoresist is spread by centrifugal force across the face of the wafer. In other instances, wafers have been dipped into a bath of photoresist for applying such photoresist to the surface of the wafer.
It will be recognized that the applying of photoresist in any of these prior methods is slow and time consuming, and there is a very substantial wastage of the photoresist. In most instances, the excess photoresist is removed from the wafer, but the wastage of the photoresist amounts to about twenty times the quantity of photoresist as remains on the face of the wafer after the process is completed.